First off, remember that the prototype S-1 (#100 in 1936 and after) and all the S-2s (#101-134) were originally built in 1906 as 1-D-1s, or 2-8-2s in steam terms, and were all rebuilt as 2-D-2s by 1909. (This was primarily an outcome of a disastrous derailment near Woodlawn, for which the running gear design got partial blame.) That would account for the differences in running gear framing. The S-3s (#135-146, built 11/08-2/09) were built as 2-D-2s, were somewhat heavier (249,800 lb. vs. 227,700 to 229,900 lb. for the S-2s) and were slightly longer in some dimensions. Electrically they were largely identical, with motors totaling 1695 hp, although the S-3s had slightly more tractive effort.
